Grainey treble huh?
As much as it 'may' stem from your DAC, other factors too might be contributing.
Without more to go on it's a tuff call as to who the culprit is.
I would suppose, as You've had this issue ongoing for some time, you've tried using different cabling, power ckts., filtration, or headphones, right? As well as the above note on a different interface apart from USB. Right?
I've found quite often, etched, hard, or grain in the highs to be the result of incoming power that hasn't been adequately addressed.
Good luck.